Soundmarks (free) is a fascinating audio recorder app. When you start and stop a recording, the app marks that point, making it easy to return to it. Think of it as an audio bookmark. The really creative part of using the app is the ability to add notes, drawings or even photos while a recording is going on. You might want to capture a whiteboard during a meeting, or add some comments. Those additions are tied to the timeline, so you can jump to any event by tapping a picture, text or drawing.
You don't have to do this live; you can add the notes or images later, at whatever place on the time line you desire. The drawing features go beyond the basics -- you can undo, delete and edit, and there are a variety of brushes to choose from.